Chapter 18 The Urinary System

Introduction Maintains homeostasis Organs Removes and restores solutes and fluids Organs Two kidneys: main filtering organs, produce urine Two ureters One bladder One urethra

Introduction (cont’d.)

Functions of the Urinary System

Functions of the Urinary System (cont’d.) Excretion: nitrogenous, drugs and toxins Maintaining blood volume and concentration Balance of water and dissolved salts pH regulation Balance of hydrogen ions

Functions of the Urinary System (cont’d.) Blood pressure maintenance Renin Erythrocyte concentration Erythropoietin: stimulates red blood cell production Vitamin D production Calciferol

The External Anatomy of the Kidneys

The External Anatomy of the Kidneys (cont’d.) Paired organs that are reddish in color About the size of a closed fist Located just above waist Between parietal peritoneum and posterior wall of abdomen Referred to as retroperitoneal

The External Anatomy of the Kidneys (cont’d.) Hilum: passage area for ureters, vessels, nerves Surrounding layers Renal capsule: innermost, barrier Adipose capsule: middle, protection Renal fascia: outer, anchors kidney

The Internal Anatomy of the Kidneys

The Internal Anatomy of the Kidneys (cont’d.)

The Internal Anatomy of the Kidneys (cont’d.) Medulla: inner area Renal pyramids: tips point inward Cortex: outer area Cortical material between pyramids Cortex and renal pyramids contain nephrons

The Internal Anatomy of the Kidneys (cont’d.) Nephrons: functional units of the kidney Minor calyx Funnel shaped, collects urine from pyramid ducts Major calyces: formed from minor calyces Join to form renal pelvis Renal pelvis narrows to form ureter

The Anatomy of the Nephrons

The Anatomy of the Nephrons (cont’d.) Nephron: microscopic renal tubule Bowman’s glomerular capsule: double-walled globe Podocytes: innermost layer Parietal layer: outermost layer Endothelial-capsular membrane: filter

The Anatomy of the Nephrons (cont’d.) Renal tubule Proximal convoluted tubule Descending limb, loop and ascending limb of Henle Distal convoluted tubule Collecting ducts

Blood and Nerve Supply to the Nephrons

Blood and Nerve Supply to the Nephrons (cont’d.)

Blood and Nerve Supply to the Nephrons (cont’d.) Renal arteries: transport 1200 mL of blood per minute Interlobar arteries Arcuate arteries Interlobular arteries Afferent arterioles divide into glomerular capillaries

Blood and Nerve Supply to the Nephrons (cont’d.) Efferent arterioles Peritubular capillaries Interlobular veins drain into arcuate vein Interlobar veins Renal veins

Physiology of the Nephrons

Physiology of the Nephrons (cont’d.) Functions Control blood concentration and volume Regulate blood pH Remove toxins from blood Stimulate red blood cell production

Physiology of the Nephrons (cont’d.) Urine formation Glomerular filtration Tubular reabsorption Tubular secretion Urine: 95% water, urea, uric acid, electrolytes 56 mL an hour is normal 30 mL an hour indicates possible kidney failure

The Ureters: Anatomy and Function

The Ureters: Anatomy and Function (cont’d.) Extensions of the renal pelvis Connect to urinary bladder Function: transport urine to urinary bladder Urine movement Peristalsis, gravity, hydrostatic pressure

The Urinary Bladder and the Micturition Reflex

The Urinary Bladder and the Micturition Reflex (cont’d.) Urinary bladder held in position by peritoneum Trigone: region between openings of ureters and urethra Detrusor muscle: three-layered smooth muscle Internal urinary sphincter: involuntary control

The Urinary Bladder and the Micturition Reflex (cont’d.) Micturition: expulsion of urine from bladder External urinary sphincter: voluntary control Bladder capacity 700-800 mL 200-400 mL: conscious of need to urinate Stretch receptors initiate micturition reflex

The Urinary Bladder and the Micturition Reflex (cont’d.) During urination Detrusor muscle contracts Muscles of pelvic floor and abdominal wall contract External urinary sphincter relaxes and urine moves from bladder to the outside

The Urethra: Male and Female Positions

The Urethra: Male and Female Positions (cont’d.) Urethra: connects bladder to the outside Females Lies directly posterior to pubic symphysis Located in wall of vagina 3.8 cm long Between clitoris and vaginal opening

The Urethra: Male and Female Positions (cont’d.) Males 20 cm long Passes through prostate gland and penis Opens at tip of penis Transports urine and semen

Animation – Urine Formation This animation presents an overview of how urine is formed [Insert Urine Formation.swf] Needs Animation introductory text and link

Summary Discussed the functions of the urinary system Described the internal and external anatomy of the kidney Discussed the structure and function of the nephron Discussed micturition and the role of the ureters and urinary bladder